1. Field of the Invention
This invention relates to an image formation apparatus which utilizes electrophotographic processes, such as a photocopying machine, fax machine, or printer, and in particular relates to a cleaning device used in such an image formation apparatus, and to a process cartridge comprising the same.
2. Description of the Related Art
Advances toward an information-oriented society in recent years have been accompanied by demands for various improvements to and evolution of image formation apparatuses, such as electrophotographic copying machines, fax machines, and printers. These demands have included faster image formation speeds, smaller equipment sizes for more efficient utilization of office space, improved image quality for transmission of high-quality information, and extended equipment lifetimes in the interest of global environmental protection. Consequently, there have been demands for faster, more responsive, smaller, and more durable photosensitive drums and other image carriers used in image formation equipment. In addition, image carriers formed with a coating layer of an organic material, with an inorganic material added to the surface of the organic material, as well as image carriers of amorphous silicon and similar, have also been used in order to extend service lifetimes.
In response to demands for higher image quality, recently it has become clear that the toner which is the developing agent is particularly effective when formed into small-diameter spherical particles. Hence toner with particles in a spherical shape of small diameter is becoming common where toner is being developed and in the marketplace. However, if toner particles are spherical in shape and of small diameter, there is the problem that cleaning of the image carrier surface becomes quite difficult. One well-known cleaning method entails using a brush to electrostatically adsorb toner remaining on the image carrier surface; because of the weak physical impact on the image carrier surface, in recent years this method has been widely adopted.
However, in this brush cleaning method, both positive and negative polarities coexist in the toner due to discharge during the transfer process in image formation; but the polarity of the voltage applied to the brush is the opposite of the toner polarity. Hence in cases where the toner has both polarities, a power supply is necessary which can apply voltages with both polarities, so that an increase in equipment cost is unavoidable. Further, in this brush cleaning method the toner which has been electrostatically captured by the brush must again be removed from the brush, and to this end numerous toner removal means must be provided.
Thus at present, a cleaning method has not yet been developed capable of accommodating a durable image formation apparatus which uses toner having small-diameter particles with a high degree of roundness.
On the other hand, as a method different from the brush cleaning method, a cleaning blade method using a blade member is also well-known, and has been widely adopted due to its simplicity and low cost.
For example, Japanese Patent Laid-open No. 9-292722 discloses an image formation method, characterized in that the electrophotographic photosensitive member is an organic photoconductive photosensitive member; the development process is a process of performing development using toner comprising a release agent with average domain diameter of 0.1 to 1.1 μm; the cleaning process is a process of performing cleaning by bringing a cleaning blade member, with an impact resilience of from 35 to 75%, into contact with the electrophotographic photosensitive member surface at an angle of from 10 to 45° in the counter direction with respect to the rotation direction of the electrophotographic photosensitive member, under a load of 5 to 40 g/cm; and moreover, the electrophotographic photosensitive member surface is processed such that the static friction coefficient of the electrophotographic photosensitive member surface with respect to the cleaning blade member is 1.0 or less.
Further, Japanese Patent Laid-open No. 5-119686 discloses a cleaning device which exhibits satisfactory cleaning performance by satisfying a fixed relation between the cleaning blade Young's modulus E, the cleaning blade thickness t, and the blade protrusion amount L, as characteristic values determining the cleaning angle during a cleaning operation.
Further, Japanese Patent Laid-open No. 2000-330441 discloses an image formation device in which the average volumetric diameter D and average roundness S of the toner particles are used to set a contact force which satisfies prescribed conditions.
Further, Japanese Patent Laid-open No. 2001-66963 discloses an electrophotographic image formation method in which cleaning is performed by causing a rubber blade to vibrate at a maximum vibration amplitude of 10 to 200 μm.
However, in the cases of all of the technologies of the prior art disclosed in the above-described publications, it is difficult to clean toner having spherically-shaped, small-diameter particles on an image carrier using a blade. In actual cleaning, the toner, blade, and image carrier are involved; if the relations between these three members are not sufficiently considered and ascertained, satisfactory cleaning results cannot be obtained. If the blade is simply pressed hard against the surface of the image carrier to form a barrier, hereafter it will be increasingly difficult to accommodate toner particles with smaller diameters.
Further, when using a blade to clean toner, having particles of high roundness and small diameter, remaining on the image carrier, because it is difficult to intercept the toner with the blade, cleaning failures tend to occur. That is, in a mechanism in which cleaning failures occur, when the image carrier moves in a state in which the image carrier and the blade are in contact, the edge portion of the fixed blade is entrained by the image carrier and lifted up. This lifting-up results in a “wedge shape”, so that the spherically formed toner particles can easily enter into the gap formed. Hence when one toner particle on the image carrier lifts the blade and passes through, succeeding toner particles also slip past continuously, and so, it is thought, a cleaning failure occurs.
In light of this, the inventors of this invention used a high-speed camera to observe the behavior of toner and the behavior of the blade during blade cleaning, and discovered that the toner particles rotate while slipping past the lower surface of the blade.